The present invention relates to a process for the formation of a di(hydroxyalkylaryl) aryl phosphate which comprises the reaction of an o-alkyl substituted aromatic diol, e.g., an o-alkyl substituted hydroquinone such as o-t-butylhydroquinone, and monoaryl dihalophosphate, such as monophenyl dichlorophosphate. The di(hydroxyalkylaryl) aryl phosphate compositions of this invention are useful as flame retardant additives for thermoplastic and thermoset resins.
The present invention also relates to certain di(hydroxy-o-alkylaryl) aryl phosphate compounds, preferably those that are p-hydroxy, such as di(p-hydroxy-o-t-butylphenyl) phenyl phosphate.
As previously described, the invention relates to a process for the formation of a di(hydroxyalkylaryl) arylphosphate which comprises the reaction of an o-alkyl substituted aromatic diol and a monoaryl dihalophosphate.
The o-alkyl substituted aromatic diol contains an alkyl substituent which can be either straight or branched chain of from one to about six carbon atoms in size. Branched structures of from three to six carbon atoms are preferred as exemplified by t-butyl. The hydroxy groups are preferably para- to one another as in hydroquinone. An especially preferred reagent for use is o-t-butylhydroquinone.
The monoaryl dihalophosphate is of the formula ArOP(O)X2, where Ar stands for substituted or unsubstituted aryl, and X stands for halo, such as chloro or bromo. The preferred aryl group is phenyl. A particularly preferred reagent to use is monophenyl dichlorophosphate.
The reaction for forming the desired compounds, which will be described in greater detail below, is between one mole of monoaryl dihalophosphate and two moles of the o-alkyl substituted aromatic diol. This reaction is preferably conducted at an elevated temperature of about 50xc2x0 C. to about 200xc2x0 C. using an effective amount (about 0.1% to about 0.5%, by weight of the diarylhalophosphate) of a Lewis acid catalyst, such as magnesium dichloride.
The reaction of the present invention also forms certain di(hydroxy-o-alkylphenyl) phenyl phosphate compounds which are believed to be novel. These compounds can be illustrated, in a preferred embodiment, by the following general formula: 
wherein, in a most preferred embodiment, both hydroxy substituents are in the para position and both t-butyl substituents, as the chosen alkyl substituents, are in the ortho position.
The resulting di(hydroxyalkylaryl) arylphosphate product can be used as a reactive type flame retardant for polymer matrices, such as epoxy and polyurethane, and as an additive or reactive-type flame retardant in thermoplastic resins, for example, in polycarbonate resin compositions, including those of the type described in U.S. Ser. No. 08/510,685, filed Aug. 3, 1995. It can be incorporated, for example, in the resin backbone.